It sets up a repeat of last year's final against the Canucks - England won 38-18 - and Saxons Head Coach Stuart Lancaster said: "I thought our scrummaging was outstanding. We gave a couple of kgs away per man but technically we were better.
"If you'd have said at the start of the game that we were going to win 41-14 I would have taken that. Our objective was to reach the final and now we want to win it - last year Canada gave us a real hard game and I am sure it will be the same this time."
Tonga will now play Italy A or Russia in the Plate final and their coach Isitolo Maka said: "It was a very tough match. I am very disappointed with the penalty tries. Without them we would have been in the game."
The Saxons broke through after just 11 minutes when referee Roman Poite lost patience with the collapsing Tongan scrum and awarded a penalty try which Rory Clegg converted.
And four minutes later they were 14-0 up when Crane picked up and drove over to give Clegg another two points.
Tonga struggled to make any inroads into the Saxons 22 with their only good run coming from centre Suka Hufanga but the move broke down.
The Saxons pack were in the ascendency as they sent the Tongan scrum upwards and backwards and Poite headed to the posts for another penalty try.
Right on halftime Clegg made it 24-0 with a penalty and the Saxons continued to turn the screw early in the second half when the fly half landed another.
However, Tonga refused to throw in the towel and they were rewarded for their endeavour to take the line-out rather than penalty kick when captain Kisi Pulu took the ball at the back and when the ball was recycled Scarlets bound- Sione Timani drove over.
But it was small respite as the Saxons forwards overpowered their opponents in another scrum and Poite awarded a hat-trick of penalty tries in the 63rd minute and Ofa Fainga'anuku was yellow carded for his sins.
Mike Brown made an impact when he came on and made a midfield break before Crane showed some deft footwork with a grubberkick for Twelvetrees to gather and score.
That was the end of Twelvetrees' involvement as he was sent to the sinbin and Pepa Kolomotangi scored a consolation try when he picked up and drove over.